Many viruses (e.g., influenza viruses, human immunodeficiency virus (HIV), and infectious bronchitis virus (IBV)) have viral envelopes covering their internal proteins and genomes. The enveloped viruses belong to many families including herpesviruses, poxviruses, hepadnaviruses, flavivirus, togavirus, coronavirus, hepatitis D, orthomyxovirus, rhabdovirus, bunyavirus, filovirus, retroviruses, and hepadnavirus, which infect both human and animals. The envelopes typically are derived from portions of the host cell membranes, where major viral glycoproteins are present on the surfaces of the envelopes to form the viral surface antigens. The viral surface antigens are typically bundled to form spikes for mediating virus entry. The spikes usually contain homotrimers of surface antigens.
Influenza A viruses belong to the Orthomyxovirus family, and have a wide host range, including humans, horses, dogs, birds, and pigs. It is an enveloped, negative-sense RNA virus composed of a set of 8 RNA segments (abbreviated as PB2, PB1, PA, HA, NP, NA, M and NS) encoding at least 10 viral proteins. The HA segment encodes the hemagglutinin (HA) protein, where the HA protein forms a homotrimer, forming the spikes on the influenza viruses.
HIV is a retrovirus. For HIV-1, there are already 33 million infected individuals who each harbor a substantial array of HIV-1 quasi-species, which results in an enormous number of variants that are simultaneously seeded and circulating in the human population. HIV contains the trimeric Env glycoprotein (gp160) on its virion surfaces.
IBV is a coronavirus, causing severe damages in poultry, contains a trimeric S protein on its surface.